My scooter's stop lights have stopped working when I apply brakes, however tail light still works. I checked for a loose connection but all seems ok. It's a Honda activa
Check the following:
the bulb: it has two filaments one can work while the other has failed
supply to the switch: if no supply check the fuse.
check the switch goes live on the output when the brake is operated.
does the socket get a supply when the brake is operated - if no and you have checked the switch then there is a break in the wire to be found.